The transition to 45 nm semiconductor fabrication technology has seen the adoption of immersion lithography for critical levels. Only immersion lithography is capable of providing the resolution to resolve the minimum pitch features at such critical levels. Immersion lithography's resolution enhancement is driven by the utilization of a higher numerical aperture lens (N.A.) which, however, results in a degradation of a depth of focus process window. This depth of focus process window can be recovered by tuning the mask stack to minimize reflectivity. Typically, a tri-layer mask stack consisting of a layer of photoresist, a silicon containing anti-reflective coating (SiARC), and an optical planarizing under-layer (OPL) is utilized to enable immersion lithography with the higher N.A. lens while minimizing reflectivity. A successful transfer of pattern thru the tri-layer mask and underlying oxide/nitride stack and subsequent need to shrink feature size critical dimensions (CD) presents a number of unique challenges for semiconductor fabrication etch. These challenges include the difficulty in maintaining CD retention thru the OPL layer and subsequent over-etch owing to isotropic characteristics during over-etch. Failure to remove the Si infused portions of the mask during the oxide etch will dictate the use of an aggressive or non-selective ASH chemistry which will subsequently lead to an attack of the exposed nitride protecting the active areas which increases the likelihood of premature exposure of the underlying NiSi to the ASH chemistry.
Accordingly, it is desirable to provide an etch process methodology which strikes a careful balance between detuning the oxide etch for mask consumption and selectivity to the mask to maintain pattern fidelity and effectively removing the remaining silicon infused polymer mask. In addition, it is desirable to provide an etch process methodology which allows for CD retention during the OPL over-etch while simultaneously enabling a partial removal of the SiARC mask to allow the use of non-aggressive ASH conditions for minimizing nitride loss. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.